strncpy() vs strncat()

Hey /prog/, I've just googled this and it returned a bunch of faggots complaining about buffer overflows.

My question is, as both functions seem to do the same thing, which one would you use?

The man page doesn't leave this clear either, it just says that strcpy zerofills the buffer.

Why would they do the same? They are analogous to strcpy and strcat. Only difference is that while strncat adds a NUL-terminator, strncpy doesn't.